"It is because the contemporary alternatives seem so one-sided and are not more evidently solutions to the problems which Thomas faced, and partly solved, that we return to him and to the tradition of theology and philosophy in which his Summa Theologiae appears: theology as the science of the first principle and this as the total knowledge of reality in its unity." -- Wayne J. Hankey, God in Himself (Oxford University Press, 1987), p.159.

Wherefore the Platonists held that "one" is a principle, just as "good" is. Hence everything naturally craves unity, just as it desires goodness. And therefore, just as love or craving for good is a cause of pain, so also is the love or craving for unity.

Not every kind of union perfects the formal aspect of the good, but only that on which the perfect being of a thing depends. Hence neither does the craving of any kind of unity cause pain or sadness, as some have maintained, whose opinion is refuted by the Philosopher from the fact that repletion is not always pleasant: for instance, when a man has eaten to repletion, he takes no further pleasure in eating; because repletion, or union of this kind, is repugnant rather than conducive to perfect being.

Separation from things hurtful and corruptive is craved, insofar as they destroy the unity which is due. Wherefore the craving for this sort of separation is not the first cause of pain, whereas the craving for unity is.

Augustine says (De Lib. Arb. iii, 23), that "from the pain that dumb animals feel, it is quite evident how their souls desire unity, in ruling and quickening their bodies. For what else is pain but a certain feeling of not wanting to suffer division or corruption?"